The present invention relates to a method and apparatus for controlling the feeding rate of fuel supplied to an internal combustion engine.
It is a well-known practice to provide an internal combustion engine with an electrically fuel-feeding rate control system. Such system calculates the fuel-feeding rate in response to the engine's operating parameters, i.e., the intake-air flow rate and engine-rotational speed, and controls the feeding rate of fuel supplied to the engine from electrical fuel-injection valves or from an electrically controlled carburetor in accordance with the calculated feeding rate.
In such a control system, when the engine is decelerating, the fuel-feeding rate is always decreased by a predetermined constant value irrespective of the change in the engine operating condition. Therefore, according to the conventional control system, optimum fuel control during deceleration cannot be expected.
Suppose the fuel-feeding rate control system has an air-fuel ratio (A/F) closed-loop device for correcting the fuel-feeding rate depending upon an oxygen concentration sensor (O.sub.2 sensor). If an engine having such a system is decelerated, since the amount of decrement of the fuel-feeding rate due to deceleration is always constant and fuel adhered to the inner wall of the intake passage is vaporized, the air-fuel mixture in the engine becomes too rich for a while, causing the emission control performance of the catalytic converter to deterorate. Then the A/F of the mixture is controlled to a desired value by the A/F closed-control operation. Namely, according to the A/F closed-loop control operation, the correction factor of the fuel-feeding rate is changed to a value by which the fuel-feeding rate is greatly decreased. During this condition where the correction factor of closed-loop control is maintained at a value by which the fuel-feeding rate is greatly decreased, if the engine is accelerated, since the correction factor cannot be quickly changed in response to the change in the engine's operating condition, sluggish acceleration and backfiring occur.